1. Field of the Invention
The present invention relates to a compound including an oxalate, a carbon dioxide absorbent including the same, a method of preparing the carbon dioxide absorbent and a method of removing carbon dioxide.
2. Description of the Related Art
Since the industrial age, energy is produced mostly using fossil fuels including coal and petroleum. However, carbon dioxide resulting from use of fossil fuels is considered mainly responsible for many environmental problems such as greenhouse effects. Thus, efforts to reduce amounts of carbon dioxide discharged to the air are continuously made all over the world so as to resolve environmental issues. One approach to overcome such environmental problems is selectively capturing and separating only carbon dioxide from exhaust gases discharged from emission sources that emit substantial amounts of carbon dioxide, such as power plants, cement factories and steel plants, and stably storing the separated carbon dioxide. This technique is commonly referred to as carbon dioxide capture and storage (CCS), and a great number of counties now make substantial investment in development of CCS technologies. CCS is divided into post-combustion capture, pre-combustion capture, and oxyfuel combustion, wherein post-combustion capture is a scheme which is immediately applicable by adding an absorption tower to a conventional emission source and thus expected to be commercially available in the nearest future. A carbon dioxide absorbent used in post-combustion capture includes alkanolamines, ammonia and ionic liquids, among which alkanolamines are widely used. Generally used amines include primary amines including monoethnaol amine (MEA) and diglycolamine (DGA), secondary amines including diethanolamine (DEA) and di-isopropylamine (DIPA), and tertiary amines including triethanolamine (TEA) and methyl-diethnaolamine (MDEA). However, these amine absorbents may need resupplying due to deterioration and evaporation issues during a recycling process after absorbing carbon dioxide. Also, when the concentration of an alkanolamine absorbent is adjusted to a high level so as to increase absorbed amount of carbon dioxide, a device is corroded and too much energy is involved in recycling the absorbent. Particularly, costs for absorbing and recycling carbon dioxide account for 70% of total CCS costs, about 70% of which is due to recycling energy, that is, about 50% of the total CCS costs account for energy for recycling the absorbent. Thus, extensive researches and developments are being conducted to reduce recycling energy of an absorbent that absorbs carbon dioxide.
There are a large number of enzymes using carbon dioxide in nature. Ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO) is an enzyme that is the most abundant in all living things. RuBisCO is an enzyme functioning in the Calvin cycle, which is involved in fixation of carbon dioxide and generates energy using fixed carbon dioxide. FIG. 1 illustrates an activated site of RuBisCO. RuBisCO includes eight large protein pieces and eight small protein pieces, in which fixation of carbon dioxide occurs actually in an active site of the large protein pieces. In detail, the active site has a structure in which a magnesium ion (Mg2+) as a metal at the center is surrounded by two carboxylic acid functional groups from amino acids, and ribulose-1,5-bisphosphate, and weakly interacts with amine of lysine.
Fixation of carbon dioxide molecule in the active site of RuBisCO is carried out through two stages. In a first stage, an amine group of lysine is coupled with carbon dioxide to form carbamate, which is then coupled with a magnesium ion (Mg2+) to stabilize coupling. FIG. 2 illustrates coupling of a magnesium ion (Mg2+), lysine and carbon dioxide in the active site of RuBisCO. In this stage, the coupling is realized only with partial pressure of a gas without addition of energy. If partial pressure of oxygen is higher than that of carbon dioxide, oxygen occupies the active site of RuBisCO, in which case RuBisCo loses activity. On the contrary, if the partial pressure of carbon dioxide is higher than that of oxygen, carbon dioxide is coupled with lysine of RuBisCO, and accordingly RuBisCO has activity.